1. Field of the Invention
This invention relates to metallurgy, and especially to metal matrix composite materials containing submicron particles and a method for their formation.
2. Description of the Prior Art
Metal matrix composite materials are generally fabricated for the purpose of improving the qualities of the matrix metal by the inclusion of sub-micron particles in the metal matrix. Usually, the desire is to improve the strength, although it may be desired to modify other qualities.
Very often, the particles may not be wettable by the matrix metal and, if this is so, the particles tend to agglomerate instead of disperse uniformly in the matrix. An example of this is the composite consisting of SiC particles in an Al matrix. The SiC resists wetting by the Al so two methods of dispersion of the SiC particles are used: (1) mechanical entrapment; and (2) high temperature. In mechanical entrapment, the Al does not adhere to the Al and the particles must be above 10 microns in diameter. If high temperature is used, the SiC reacts with the Al to form Al.sub.4 C which is very brittle and the smaller the particles of Si Care, the more Al.sub.4 C is formed.
To date, attempts to cast most metal matrix composites have been unsuccessful because of non-wetting of the reinforcement particles which, in turn, results in agglomeration of the particles. To disperse the particles, high temperature and excessive agitation have been used, resulting in partial decomposition of the reinforcement particles. High heat applied to SiC particles causes decarburization, reducing the strength of the SiC particles and, as stated before, forms brittle Al.sub.4 C.